ML20042C018

Advises of Delay Until 1983 Refueling Outage for Installation of Reactor Coolant High Point Vent Sys Per NUREG-0737 Item II.B.1.Delay Caused by Revised Design of Pressurizer Vent.Revision 2 to Design Criteria Encl

ML20042C018
Person / Time
Site:	Davis Besse
Issue date:	03/23/1982
From:	Crouse R TOLEDO EDISON CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.B.1, TASK-TM TAC-44364, NUDOCS 8203300077
Download: ML20042C018 (5)

Text

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l Docket No. 50-346 TOLEDO License No. NPF-3 EDISON Serial No. 795 Roo.no P. Csouw vo w

%A; bd March 23, 1982 aim a.,mi m

Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz @

R QN ^ < 1x Operating Reactors Branch No. 4 y \

Division of Licensing N

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United States Nuclear Regulatory Commission Washington, D.C. 20555 s

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Dear Mr. Stolz:

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Previous Toledo Edison letter dated February 27, 1981 (SerialsNo. 692) - '

discussed installation of a Reactor Coolant High Point Vent Sy};tiem foEthe.

Davis-Besse Nuclear Power Station Unit 1 (DB-1). This was a partial-'~

response to your letters of September 13, and October 30, 1979 concerning gj implementation of lessons learned from Three Mile Island, Unit 2 (TMI-2) incident. Toledo Edison proposed that the vent on the pressurizer will be routed to the containment atmosphere in an unobstructed area.

This letter is to identify a revision in the design of the pressurizer vent. The design now provides for the vent to be routed to the pressurizer quench tank. This supercedes the other previous pressurizer vent design route to the containment atmosphere. The attachment is the Reactor Coolant Ifigh' Point Vents System design criteria revised to reflect this design. Figure 2 reficcts the revised conceptual drawing.

In a letter to Mr. D. G. Eisenhut dated December 30, 1980 (Serial No. 670) concerning Clarification of TM1 Action Plan Requirements (NUREG 0737)

Toledo Edison committed to installation of vents during the first refueling outage af ter January 1, 1982 (Item II.B.1). This change in the design of

' the pressurizer vent will. delay the installation of this vent from the 1982 refueling' outage (presently scheduled to end in June 1982) to the 1983 refueling outage. The hot leg vents will be installed during the present 1982 refueling outage.

Very truly yours, ffh+w 1 RPC:RLW  !

Attaciunent cc: DB-1 NRC Resident Inspector pk a/6 THE TOLEDO EDISON COMPANY- EOISON PLAZA 300 MADISON AVENUE TOLEOO. OHIO 43652 8203300077 820323

-PDR ADOCK 05000346 P PDR

Docket No. 50-346 License No. NPF-3 Serial No. 795 March 23,1982 Page One of Four REACTOR COOLANT llIGH POINT VENTS SYSTEM DESIGN CRITERIA (Revision 2)

The proposed Reactor Coolant System (RCS) liigh Point Vent System provides vents on each of the two hot legs and on the pressurizer. Each vent line will be controlled by two valves from the control room using individual handswitches and each valve will have positive position indication in the control room. The two hot leg vent lines will have restrictive orifices sized such that the flow rate will not exceed the RCS makeup system capability and the vents will be routed to the containment atmosphere in an unobstructed area. The vent on the pressurizer shall also be designed and sized such that the inadvertent opening of both valves could not cause the RCS to depressurize when all pressurizer heaters are energized. The vent on the pressurizer will be routed to the pressurizer quench tank.

The conceptual drawings (Figures I and 2) of the system is provided.

The vent on each hot leg will be controlled by two solenoid operated valves. The valves will be nuclear Class 1 and will be seismically and environmentally qualified to the criteria of the DB-1 FSAR. The valves will be powered from Class IE power supplies. The two valves on loop 1 line will receive channel 1 AC and channel 1 DC power, respectively. The two valves on loop 2 will receive channel 2 AC and channel 2 DC power, respectively. The AC valves will utilize control penetrations, while the DC valves will utilize power penetrations through the containment vessel.

Also, the channel 1 AC control circuits and power circuits between the motor control centers and the valves will be separated from the channel 1 DC circuits. The same will be done for the channel 2 circuits. There-fore, all cabling will be kept separate for all four valves. This will be done to maintain channel separation and to prevent the possibility of hot shorts causing inadvertent opening of both of these vents. The valves will fail closed on loss of power.

The high point vent from the pressurizcr will be installed as shown on Figure 2. Existing valve IIV-239A is presently powered from a channel 2 Class IE supply. Existing valve IIV-200 is presently powered from a non-lE supply, but will be modified to be powered from a channel 2, Class lE supply. All power circuits between the motor control centers and the valves and all control wiring for IIV-200 and IIV-239A will be separated to prevent the possibility of hot shorts inadvertently opening both valves.

To utilize the high point vent on the pressurizer, these valves would be opened from the control room.

All taps for the new vent lines and all associated valving and instrumen-tation will be located above the maximum credible water level in the containment vessel and will be protected against damage from adjacent systems.

As discussed in the Davis-Besse Unit 1 FSAR, Section 6.2.5, the flammability limit (4%) for hydrogen generated in accordance with Regulatory Guide 1.7 is not reathc4 until 37 days after the postulated accident. The FSAR

a Docket No. 50-346 License No. NPF-3 Serial No. 795 March 23,1982 Page Two of Four analysis assumes that all the hydrogen from the metal-water reaction is released from the Reactor Coolant System to the containment in the first two minutes after the accident. Therefore, it is concluded that this analysis envelopes the case where hydrogen could be released into the containment over a longer period of time due to RCS high point venting.

The system 9 ,a as described above has considered the effects of single failures, inte. action with adjacent systems that could cause missiles, water levels in the containment vessel after a LOCA and fire. The high point ver.t valves are located so that they will not be affected by missiles or high water level. The separation assures that a fire would not cause inadvertent opening of a vent path, or failure of a vent path if needed. The electrical design assures that a single failure, including interruption of a power supply or hot shorts, will neither prevent the ability to vent through at least one high poirt vent nor cause the inadvertent opening of any high point vent. Redandancy of one reactor coolant loop vent is provided by the other hot leg vent. The primary vent path for the pressurizer is the installed Pilot Operated Relief Valve ,

(PORV). The additional pressurizer vent described here will provide a back-up capability for that path, ds e/l

Dock t No. 50-346 Pcg2 Threa of Four -

Licenze No. NPF-3 Serial No. 795 .-

March 23, 1982

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